1. Field of the Invention
The present invention relates to an optical module and a communication-apparatus-use cage.
2. Description of the Related Art
An optical module has been popularly used for communication between apparatuses or between stations, and a plurality of optical modules are used in the inside of one apparatus depending on a case. In the use of the optical module, there may be a case where an amount of electromagnetic interference (EMI) generated by the module causes a problem. An amount of electromagnetic interference to a digital electronic apparatus is regulated by an organization such as Federal Communications Commission (FCC) in the United States of America, and is regulated by an organization such as International Special Committee on Radio Interference (CISPR) in Europe. In the optical module, there may be a case where a plurality of optical modules are used in one apparatus and hence, to regulate an amount of radiation of EMI within a limited value, it is necessary to suppress the EMI radiation from the optical module to a minimum value.
To reduce an amount of radiation of EMI from an optical module, as a conventional method which overcomes this drawback, there has been known a method where a metal collar provided with spring fingers is arranged around the optical module. Alternatively, there has been known a method where a metal color provided with spring fingers is arranged on an inner side of a cage which houses an optical module therein. In both structures, the optical module and a cage into which the optical module is inserted are electrically connected with each other by the metal collar. Particularly, in the U.S. Pat. No. 7,928,324 specification, there is disclosed a method where a space between an optical module and a cage is hermetically sealed by a metal collar, and a space between the metal collar and the optical module is embedded with a conductive gasket so that the electrical connection among the cage, the metal collar and the optical module is strengthened whereby an amount of radiation of EMI is reduced.
However, it is difficult in an actual practice to hermetically seal the space between the optical module and the cage by the metal collar or the conductive gasket and hence, there has been a case where an amount of radiation of EMI cannot be sufficiently reduced by the metal collar or the conductive gasket.